Many diseases of the body are caused by a deficiency of certain endocrine gland hormones. These diseases include myxedema and diabetes mellitus. The endocrine glands are usually considered to include the thyroid, parathyroid, thymus, pituitary, pineal, adrenal, pancreas and the gonads. While a few hormones, e.g. thyroid hormone, may be taken orally, most hormones are digestable and must be injected.
There are several disadvantages with periodic injection of hormones. Since injections are painful and troublesome, and each injection represents a possibility for infection, injections are spaced at intervals as far apart as possible, resulting in peak and valley hormone concentrations. It has been found that more effective treatment results from a constant supply of hormones in accordance with the body's need. Constant control of the hormone level avoids the problems of peaks and valleys in medication.
To date, the best known detector to measure the body's demand for a particular hormone is the cell of the gland which produces that hormone. Such a cell not only measures the body's need, but also produces the necessary dosage of that hormone. The advantages of such cells are readily apparent in the case of diabetes and insulin demand.
Diabetes mellitus is a disease characterized by hypoglycemia, polyuria, and wasting. It is beneficial to maintain normal blood glucose levels in diabetics at all times, an objective difficult or impossible to achieve using insulin injection and diet. Two solutions have been suggested for achieving more physiologic patterns of insulin replacement. One approach uses a glucose sensor operably associated with an insulin injection system. A second approach implants live insulin producing tissue within the patient.
Transplantation of pancreatic tissue has met with limited success because of immune rejection reactions encountered due to the difficulty in obtaining a perfect tissue match. One solution to this problem is to encapsulate live hormone-producing cells within a membrane capsule as shown in U.S. Pat. No. 3,093,831 to Jordan. The membrane protects the cells from such reactions but allows the free passage of hormones and nutrients. The encapsulated hormone-producing cells can then either be injected or surgically implanted. For various reasons encapsulated cells once placed in the body only have a limited life span, usually measured in weeks.
Other methods have been to place insulin cells on one side of a membrane while blood flows on the other side of the membrane. However these devices are for extracorporeal use which has limits on blood flow access and these devices are not readily adaptable to implantation.
Since no means is presently known to keep implanted pancreatic cells alive and producing insulin at a useful rate indefinitely, periodic replacement is necessary. However, none of the previous implantable allows easy replacement of the cells from outside the body. What is needed is a method and structure for replacing live pancreatic islet cells or other hormone-producing cells from outside the body without having to surgically remove the entire implant.
This invention provides a system and method yielding an artificial endocrine gland with replaceable hormone-producing cells. This invention also provides a system and method yielding an artificial endocrine pancreas which utilizes live pancreatic islet cells as the hormone-producing cells.